Reference is made to a book authored by N. J. Harrick entitled "Internal Reflection Spectroscopy", published by Interscience Publishers in 1967. This book provides a complete description of the principles underlying this technology, and also describes the construction and configuration of so-called internal reflection elements (IREs) used in such analysis equipment. Attention is especially drawn to pages 223-227 which describes the application of IREs for use in liquid cells. Reference is further made to U.S. Pat. Nos. 4,730,882 and 4,602,869, which are also directed to different IRE and liquid cell geometries, the contents of which are hereby incorporated by reference.
In general, it is important to many companies that process liquids to be able to conduct in-line analysis or analyses of samples in the simplest and most economic manner. As is known, many conventional spectrometers generate a radiation beam which upon emerging from the instrument converges to a region in the so-called sampling space or compartment of the instrument, and if not intercepted or used will continue back into the instrument for detection and spectral analysis. It is common to locate the IRE element and transfer optics for the IRE element in an accessory in the sampling space so as to maintain the original focussing conditions. At the same time, it is desirable that the IRE element, which must physically contact the liquid, be suitably positioned for effective and efficient use.
The U.S. Pat. No. '869 referenced above describes a single reflection prism liquid cell for IRS. This construction offers limited interactions with the liquid sample and thus reduced signal-to-noise (S/N) ratios. A recent paper in Applied Spectroscopy, Vol. 44, No. 1, 1990, pps. 50-59, describes a cylindrical IRE cell using an IRE rod with a circular cross-section, which can be located in line with the optical beam in the sampling compartment. Disadvantages, however, of this construction include reduced light throughput due to the need for the entering and exiting beam to reflect off metallic surfaces, and the possibility of spurious spectra due to beam interaction with the seals for sealing the IRE rod within the cell.